Wireless transceivers are calibrated to mitigate and compensate for errors introduced by the electronic signal processing components in the transceivers. During calibration, a signal having some known properties is injected into the transceiver. Adjustments are made to components in the transceiver based on signals generated by the components in response to the calibration signal. In some instances, the signal is a “calibration signal” that has properties that make it similar to a signal that is processed by the transceiver during normal operation. In other instances, the signal is a “noise signal” that simulates white noise or some other type of noise.
One type of error experienced by quadrature transceivers is IQ mismatch. The quadrature receiver downconverts a quadrature baseband signal from a radio frequency (RF) signal to a quadrature baseband signal. More specifically, the receiver includes a mixer that mixes the RF signal with an in-phase component of a local oscillator signal to downconvert the radio frequency signal to an in-phase component (i.e., the “I” signal) of the quadrature baseband signal. The mixer also mixes the RF signal with a quadrature component of the local oscillator signal to downconvert the radio frequency signal to a quadrature component (i.e., the “0” signal) of the quadrature baseband signal. The I signal and the Q signal are processed on separate paths of components within the receiver before being recombined for demodulation.
However, the gain of the components in the I path and the Q path may not match exactly. As a result, a gain error is introduced into the quadrature baseband signal. In addition, the in-phase component and the quadrature component of the local oscillator signal used by the mixer for downconversion may not be exactly ninety degrees out-of-phase. As a result, a phase error, or quadrature error, is introduced into the quadrature baseband signal. Combined, the gain and quadrature errors form an I/O mismatch error in the receiver. It is desirable to correct the I/O mismatch of the receiver in baseband in order to provide improved performance.